Some modules in trove.extensions can't be imported as they are blocked by files used for Oslo extensions feature.

We need to add an extension at Rackspace but can't because we can't import anything in the directories sitting at trove/extensions because there are files named the same thing as the directories. For example, "from trove.extensions.mgmt import models" fails because it imports the file "trove/extensions/mgmt.py" and stops. We could move this to "trove/extensions/mgmt/__init__.py" but have an issue because the current extensions code works not by doing real Python imports but looking for files. Thus, the extension *files* could be moved to contrib/extensions.